Proper Noun.
1. One of several popular nicknames given to the most thrilling basketball player in the NBA, Gilbert Arenas. A two time all-star renowned for his ability to score as time in quarters, halves, and especially games expire, Agent Zero currently stars at guard for the Washington Wizards. Agent Zero sports the jersey number 0 because he was told as a high school player that he would spend exactly zero minutes on the court as a college player.

The sneaky inserting of a finger or thumb (agent) into the anus (the zero) of a sexual partner. It is paramount that the receiver is not aware of the agent (finger or thumb), and that the zero (anus) is penetrated sneakily without early detection.

Guy 1: "Yo last night I gave her an Agent Zero! She never expected it until it was in!"

Guy 2: "No way, she never knew it was coming!?"
Guy 1: "Not until my finger was in her anus!"